Wireless direction finding system



mm 16, 1941- c. F. A. WAGSTAFFE I WIRELESS DIRECTION FINDING SYSTEM Filed June 9, 1938 Z Sheets-Sheet -1 ArraR/VEY ec. w, 1941. v c. F. A. WAGSTAFFE 2,266,454 I I WIRELESS DIRECTION FINDING SYSTEM 2 Sheets-Sheet 2 Filed June 9, 1938 727 C/M/VNEZ I 27 LIMMVEL I ATmRA/E) Patented Dec. 16, 1941 .WERELE S S DERECTKON PENDING SYSTEM Application June 9, 1938, Serial No. 212,658 In Great Britain July 9, 1937 i filaiins. (Cl. 250-11) This invention relates to radio direction find- Three embodiments of the invention are iling apparatus of the type employing angularly, lustrated in the accompanying drawings, in disposed stationary aerials as for example, Adwhich; Fig. 1 shows an arrangement using a cock direction finders. goniometer with a single earch coil; Fig. 2

One of the limitations as regards sensit v y 5 shows an arrangement similar to Fig. 1 in which and range, with this type of direction finder, is separate search coils are used; and Fig. 3 shows due to the effective pick-up of the aerial system, a search coil arrangement permitting conversion taken as a whole, being small. This arises from of three channels into two channels. the fact that each pair of aerials is connected In Fig. l is shown a three-pair arrangement at the goniometer or other detecting arrange- 10 comprising three pairs of aerial I, l, 2, 2' and ment in such a way that the current flowing in 3, 3' and three field coils, A, B, C associated with the detecting device is due to the vectorial diia single search coil SC. Alternatively, the ference of signals from the two aerials of the goniometer may be built up in three separate pair. sections consisting of three field coils A, B, C For a signal (ground wave) arriving along the 5 and three search coils, SCI, S02, S93, the latter line joining the two aerials of a pair the magniconnected in series or parallel and mounted on tude of the diiierence vector for that pair is a common spindle, as shown in Fig. 2 (series arproportional to: rangement). For the purpose of illustrating the 1rd method, connections of a simple kind have been 2E sin .20 shown between the aerials and goniometer field coils. It must, of course, be understood that Where any usual system can be used here. d: distance between the 9311515 t can be shown that with such an arrange- E the signal E. M. F. in one aerial alone. u if t pacing b t i 1 of pair If t Vector s p opor o to 25 is increased to give the maximum possible total It is clear that as d/A increases the vector does signal 1, to /g th ximum rr due t also until it reaches a maximum when d/ thi large spacing i less t 1/ h difier- However, with ordinary systems of indication, m vector previously ti d 111 w b using a oni me er or an os illosraph, t is not I proportional to an. In addition to this gain Dermlsslble t Increase d/k beyond a Ce ta there is also a gain due to more energy being figure, for otherwise an error is introduced in absorbed from the signal wave by the larger the indicated bearing. This error is octantal in number of aerials. For a ground Wav the total nature and, in order to limit it to ion a gain over the orthodox system with 0.1a A spacground wave, it can be shown that d/A must ing will be approximately 10 db. For a downnot exceed about 0.14. For a downcoming wave coming ray of angle of incidence 45 (where the and a given value of d/x the error is smaller and effective spacing is reduced), the gain will be depends upon the angle of incidence of the approximately 11.5 db. All of this gain is availdowncoming wave. So that exceeding the figure able for giving increased sensitivity and thus inmentioned for d/k and correcting for the error creased range where static level is not the limitby calibration is not possible because of the ing factor.

varying nature of the error with varying angle By using four pairs of aerials or more, the of incidence. maximum error is till further decreased though,

The ob ect of the present invention is to inas mentioned, three pairs give so small a maxicrease the effective pick-up without introducing mum error that further reduction here is not error. It should, of course, be understood that of any practical advantage. However, four pairs the pick-up can be increased in this way by inwill give further pick-up and also make it poscreasing the actual height of the acrials, but sible to use, if desired, two goniometers of standthere is a practical limit to this course on acard type with search coils in series or parallel count of cost in the case of long waves and on and spindles coupled and field systems set at account of electrical reasons on short waves. 45 to each other. It is also possible with four According to the present invention, it is prcpairs to increase the spacing to greater than posed to use three or more pairs of aerials spaced \/2 to, for example, 0.75 A, without exceeding equally round a circle. These are connected to of error (under the worst conditions, i. e. on a a goniometer with a number of field windings ground wave) so that with a downcoming wave equivalent to the number of pairs of aerials. the effective spacing is more nearly equal to- M2 and a still greater gain over the usual type of aerial system is obtained. This arrangement would be useful for short wave long distance direction finding.

In an orthodox manner an extra aerial can be employed in order to determine the sense of the bearing.

The aerial system of Figs. 1 and 2 can be used with an oscillograph indicator by using three separate amplifying channels and an oscillograph with three pairs of deflecting plates with deflecting axes at 0, 120 and 240 Alternatively, the three channels conveying the hearing information from the aerials can be transformed into two channels for connecting to an orthodox two-amplifier system in order to produce the bearing indication on an oscillograph. Again, alternatively and preferably the two channels can be connected to a single amplifier arrangement as described in United States application Ser. No. 209,186, filed May 21, 1938, Patent No. 2,213,874, granted Sept. 3, 1940.

One type of circuit for converting from three channels to two channels is shown in Fig. 3, though many others can be devised, all, however, depending upon the same general principle. Along the same lines circuits can be produced for converting to two channels from any number of aerial pairs and associated channels.

In Fig. 3, T1, T2 and T3 are three special transformer; in which the secondaries A and B have zero direct coupling between each other and in which the remaining couplings are as follows:

The primaries P1, P2 and P3 are identical and also of the secondaries A1- -A.2=A3=B1==B2=Bs.

It should be noted that, apart from the increase of pick-up obtained by the system outlined, the latter has an advantage over the normal system in that it is less dependent upon a critical balance between the aerials of a pair, particularly with respect to phase. Consideration of the vector diagrams will show this.

The aerial system is also applicable for transmission, for example, to a beacon using an Adcock type aerial fed by a transmitting goniometer. For instance, a transmitting beacon of the A-N type, with approach paths of direction variable at will, would be provided by using an arrangement as Fig. l with the modification of an additional search coil wound on the same rotor as the first but at right angles (or at any other angle as required by the approach paths) to it. There would then be arrangements of an orthodox kind to connect the transmitter for the A periods to one rotor coil and for the N periods to the second. Such an arrangement would give a less critical balance of aerials for a given stability of equisignal lines, and a greater field strength at a given range with a given transmitter power, compared with a similar arrangement utilising a twopair aerial system of small spacing and a goniomete having two field windings.

What is claimed is:

1. A directional radio receiving or transmitting system in which the aerial system comprises at least three pairs of aerials equally spaced around a circle and angularly related so that the planes defined thereby intersect at the center of said circle, a separate coil coupled between the aerials of each pair, and movable energy transfer means coupled to said coils comprising at least three search coils angularly disposed in the same relation to one another as the planes defined by said pairs of aerials.

2. A directional radio receiving or transmitting system according to claim 1 wherein said search coils are mounted on a common axis.

3. A directional radio receiving or transmitting system as claimed in claim 1, comprising three pairs of aerials in which the aerials of each pair are spaced apart, a distance substantially equal to one half the working wavelength.

4. A directional radio system, comprising at least three pairs of aerials equally spaced around a circle, a goniometer device comprising separate field coils connected to each pair of aerials, a corresponding plurality of angularly arranged search coils coupled respectively to each of said separate field coils, and a second corresponding plurality of search coils arranged at right angles to the respective first named search coils and coupled respectively to each of said field coils, a channel connected to said first named search coils, and a second channel connected to said second named search coils.

CHARLES FREDERICK ALLEN WAGSTAFFE. 

